Statistical analyses were carried out on the data obtained under strictly controlled conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows, and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2–6 months earlier and whose daily milk production ranged from 11 to 20 kg.

The authors have calculated and studied the correlations between faecal and urinary sodium losses, sodium excretion in the milk, digestible sodium and sodium balance and the 75 other nutritive factors which were analysedfor each of the 55 above mentioned experimental diets.

The most important factor in the fate of sodium is the amount of dietary sodium. Sodium digestibility is neither total nor constant: faecal losses and digestible amounts are enhanced when sodium intake is increased and faecal losses are also positively correlated with dry matter and nitrogen intakes. An increase in digestible sodium benefits both urinary excretion and balance, the latter being reduced by an increase in dry matter and nitrogen intake.

Sodium balance is always negative when sodium content of the diet is lower than 0.1% in the dry cows and 0.2% in the lactating cows. In our experimental conditions, the sodium requirements for milk production do not influence sodium digestibility, but are met above all to the detriment of urinary losses.